This proposal is designed to assess several of the etiologic mechanisms involved in the altered vascular reactivity that accompanies normal pregnancy. Using pregnant and non-pregnant animals we will examine local vascular reactivity in an isolated, chemically denervated, hind limb perfusion preparation. We will examine baroreflex activity using both a chronic and acute isolated carotid sinus preparation. These studies are also designed to evaluate the effects of the endocrine status of the animal on vascular reactivity and baroreceptor function. In the hind limb preparation, muscle vascular resistance changes will be measured in response to angiotensin II and alpha-receptor stimulation in ovariectomized, ovariectomized-progesterone treated and pregnant animals. In the chronic and acute isolated carotid sinus baroreflex preparation baroreflex activity will be assessed by examining the immediated transient response in heart interval to alterations in carotid sinus pressure and the steady state changes in heart interval and total peripheral resistance during the same pressure alterations. The significance of this proposal is that it is the first to attempt the dissection of the various mechanisms involved in the altered pressor response to vasoactive stimuli that occurs in normal pregnancy. This will provide a data base for exploring hypertensive disorders of pregnancy in which there is an absence of this reduced vascular reactivity.